1. Field of the Invention
The present invention relates to a method and a device for calibrating a torque measurement unit that is connected with a dynamometer, whereby the torque measured by the torque measurement unit and that of a reference measurement device is compared for calibration.
2. The Prior Art
On test stands for vehicles or vehicle components such as, for example, transmissions, power trains, combustion engines, etc., the test specimen is driven or charged by an dynamometer, a so-called dyno, in order to simulate certain operating conditions for the test specimen. To do so, as a rule, a number of sensors are also used in order to capture various measurement values. In particular, in such test stand structures, driving speed sensors and torque sensors are used. While the number of rotations can be measured very precisely with various methods, as a torque measurement unit for the measurement of the torque, often so-called torque measurement flanges are used, which are mounted between the driven shaft of the dyno and the drive shaft of the test specimen. But dynos that are mounted to oscillate are also known, in which as torque measurement unit, for example, a beam in bending or a load cell are used, which measure the force between stator and the machine housing, by means of which the acting torque can be inferred. Torque measurement units must, however, be calibrated in order to make precise measurements possible. The calibration must also be regularly repeated during running operation. For this, numerous methods exist in the prior art as to how such a torque measurement unit such as, for example, a torque measurement flange, a beam in bending or a load cell can be calibrated.
Frequently, calibration levers are used that are affixed to a lever mounted at the shaft, to which at a certain distance a certain weight is mounted, and by means of which a defined torque is generated that is captured by the torque measurement unit. Due to the determination of the difference between the measured value and the introduced value, the torque measurement unit can subsequently be calibrated. An example of this can be found, for example in WO 2006/099641 A1. But as a result of such a calibration lever, bending and horizontal forces are also always introduced, which can falsify the measurement result.
From DE 10 2007 040 106 A1 a calibration unit is known in which the electric motor is connected to the torque measurement device by means of a transmission, here a torque measurement flange. Thus, for calibration by means of the electric motor and the transmission, a certain torque can be introduced, which is measured by the torque measurement unit, but whereby for calibration, the performance brake must be blocked. But the calibration unit is also costly in design and due to its size and weight, it is also difficult to handle.
It is further known of machine tools, for example, from U.S. Pat. No. 4,483,177, to use the drive motor of the machine tool itself for generating the torque for calibration of the torque sensor. However, for machine tools, significantly lower precision is required. For this reason, here, only a certain speed is specified at which a screw nut on a threaded spindle drives against a stop, as a result of which a certain torque is created, which can be measured by the torque measurement unit and a reference torque measurement device and subsequently compared for calibration. But it is not possible here (and also not necessary) to set any kind of precise calibration torques.
However, high demands on precision must be satisfied in a test stand environment. For the calibration of the torque measurement unit at a precision that is sufficient for test stand applications, the torque must be applied in suitable form during the measurement (and/or calibration). In order to be able to determine the hysteresis of the torque measurement unit that is to be calibrated and to not destroy it, the applied torque is to have as little waviness as possible and preferably no excess oscillation. Moreover, torque measurement units are, as a rule, calibrated within a certain calibration range and are not calibrated only at an individual torque, which makes it necessary (within the possibilities) that any calibration torques are specified. In particular, in a test stand environment, certain safety provisions must also be made. For example, when a shaft breaks, the dyno may not continue to drive uncontrolled, but must be stopped immediately. Therefore, it is not sufficient for calibration with the drive motors to simply specify a torque for the drive motor, as the drive motor would run away uncontrolled in the event of a broken shaft.
It is therefore the objective of the present invention to provide a method and a device for calibrating a torque measurement unit that is simply constructed, sufficiently precise and can also be handled easily, while making a flexible specification of the calibration torques possible and also satisfying the safety requirements.